..and speaking of religious books, have a look at this series of classic Christian writings published by Hodder in the UK. The covers are designed by Stuart Bache (last posted about here). You would not think that a colour scheme that was predominantly grey would be so eye-catching.
And my favourite, by a Nineteenth-Century minister and Darwinian, with a lovely 'profusion of life' cover:
UPDATE: The final cover above is actually by Mark Read, Senior Designer at Hodder, while the Bible cover below was designed by Crush.
Which reminds me of this Hodder-published Bible from a little while back, with a clever, gorgeous and funny/sad cover: